Uplink OFDMA processing in WLANs

ABSTRACT

This disclosure relates to orthogonal frequency division multiple access (OFDMA) communication in wireless local area networks (WLANs). According to some embodiments, a downlink OFDMA frame may be transmitted. An uplink OFDMA frame including acknowledgements associated with the downlink OFDMA frame may be received. The uplink OFDMA frame may be processed, in some instances including determining which devices receiving the downlink OFDMA frame transmitted an acknowledgement associated with the downlink OFDMA frame in the uplink OFDMA frame.

PRIORITY INFORMATION

This application claims priority to U.S. provisional patent applicationSer. No. 62/101,913, entitled “OFDMA Communication in WLANs,” filed Jan.9, 2015, which is hereby incorporated by reference in its entirety asthough fully and completely set forth herein.

FIELD

The present application relates to wireless communication systems,including orthogonal frequency division multiple access (OFDMA)communication in wireless local area networks (WLANs).

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. Forexample, wireless local area network (WLAN) accessibility is expected inmost communication devices. WLANs are also increasingly being used tooffload communication from cellular networks and/or base stations. Inview of the expected continued increase in WLAN deployment and usage,existing WLAN communication techniques may provide insufficient capacityand flexibility relative to demand. Accordingly, improvements in thefield are desired.

SUMMARY

Embodiments described herein relate to devices, systems, and methods fororthogonal frequency division multiple access (OFDMA) communication inWLANs.

According to the techniques presented herein, it may be possible formultiple wireless devices to perform WLAN communication using OFDMAtechniques. As one such possibility, it may be possible to performuplink OFDMA communication, e.g., at least for acknowledgments to adonwlink OFDMA frame. For example, a downlink OFDMA frame structure maybe configured such that the packet lengths provided to each recipient ofthe OFDMA frame are equal (e.g., by padding payloads of some of thepackets as needed to obtain matching packet lengths). Transmission ofacknowledgements by those recipients back to the original transmittingdevice may as a result be sufficiently synchronized in time as to enableconcurrent reception of those acknowledgements. The acknowledgements mayfurther be coordinated to be transmitted on the same bandwidth portionsallocated for the downlink communication being acknowledged. Under suchcircumstances, the acknowledgement transmissions may have the same (orsufficiently similar) spectral mask as the downlink OFDMA frame beingacknowledged and may effectively form an uplink OFDMA frame.

The techniques described herein may be implemented in and/or used with anumber of different types of devices, including but not limited toaccess points, cellular base stations, smart phones, tablet computers,wearable computing devices, media players, set-top boxes, and any ofvarious other computing devices capable of wireless communication.

This summary is intended to provide a brief overview of some of thesubject matter described in this document. Accordingly, it will beappreciated that the above-described features are merely examples andshould not be construed to narrow the scope or spirit of the subjectmatter described herein in any way. Other features, aspects, andadvantages of the subject matter described herein will become apparentfrom the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present subject matter can be obtainedwhen the following detailed description of the embodiments is consideredin conjunction with the following drawings, in which:

FIG. 1 illustrates an example (and simplified) wireless communicationsystem;

FIG. 2 illustrates an example block diagram of a mobile device;

FIG. 3 illustrates an example block diagram of an access point;

FIG. 4 is a flowchart diagram illustrating an exemplary method forperforming OFDMA communication in a WLAN;

FIG. 5 illustrates an example spectral transmit mask configuration forWLAN OFDMA communication;

FIG. 6 is a frequency/time diagram of an example downlink and uplinkWLAN OFDMA transmission;

FIG. 7 is a frequency/time diagram of an example uplink(acknowledgement) WLAN OFDMA transmission;

FIG. 8 illustrates an example waveform related to preamble processing ofan uplink WLAN OFDMA packet;

FIGS. 9A-9B illustrate example autocorrelation performed at the L-STFportion of an uplink WLAN OFDMA packet;

FIG. 10 illustrates an example frequency offset and correction per userconfiguration for uplink WLAN OFDMA communication;

FIG. 11 illustrates an example logical block diagram for CFO estimationuplink WLAN OFDMA communication;

FIG. 12 illustrates an example of possible frequency offset correctionresults for a BPSK uplink WLAN OFDMA communication; and

FIG. 13 illustrates example CDF plots of channel estimation withfrequency offset correction for uplink WLAN OFDMA communication.

While the features described herein may be susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION Acronyms

The following acronyms are used in the present disclosure.

BS: Base Station

AP: Access Point

APN: Access Point Name

LTE: Long Term Evolution

RAT: Radio Access Technology

TX: Transmit

RX: Receive

WLAN: Wireless Local Area Network

I-WLAN: Interworking WLAN

SIP: Session Initiation Protocol

PDN: Packet Data Network

PGW: PDN Gateway

SGW: Signaling Gateway

ePDG: evolved Packet Data Gateway

GPRS: General Packet Radio Service

Terms

The following is a glossary of terms used in this disclosure:

Memory Medium—Any of various types of non-transitory memory devices orstorage devices. The term “memory medium” is intended to include aninstallation medium, e.g., a CD-ROM, floppy disks, or tape device; acomputer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. The memory medium mayinclude other types of non-transitory memory as well or combinationsthereof. In addition, the memory medium may be located in a firstcomputer system in which the programs are executed, or may be located ina second different computer system which connects to the first computersystem over a network, such as the Internet. In the latter instance, thesecond computer system may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums which may reside in different locations, e.g., indifferent computer systems that are connected over a network. The memorymedium may store program instructions (e.g., embodied as computerprograms) that may be executed by one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems or devices which are mobile or portable and which performswireless communications. Examples of UE devices include mobiletelephones or smart phones (e.g., iPhone™, Android™-based phones),portable gaming devices (e.g., Nintendo DS™, PlayStation Portable™,Gameboy Advance™, iPhone™), laptops, PDAs, portable Internet devices,music players, data storage devices, other handheld devices, as well aswearable devices such as wrist-watches, headphones, pendants, earpieces,etc. In general, the term “UE” or “UE device” can be broadly defined toencompass any electronic, computing, and/or telecommunications device(or combination of devices) which is easily transported by a user andcapable of wireless communication.

Mobile Device—any of various types of communication devices which aremobile and are capable of communicating on a cellular network and anon-cellular network, such as WLAN. A UE is an example of a mobiledevice.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless cellular telephone system or cellular radio system.

Access Point—The term “Access Point” has the full breadth of itsordinary meaning, and at least includes a wireless communication devicewhich offers connectivity to a wireless local area network (WLAN), suchas a Wi-Fi network.

WLAN—The term “WLAN” has the full breadth of its ordinary meaning, andat least includes a wireless local area network technology based on theIEEE (Institute of Electrical and Electronics Engineers) 802.11standards, and future revisions or enhancements to those standards.

Processing Element—refers to various elements or combinations ofelements. Processing elements include, for example, circuits such as anASIC (Application Specific Integrated Circuit), portions or circuits ofindividual processor cores, entire processor cores, individualprocessors, programmable hardware devices such as a field programmablegate array (FPGA), and/or larger portions of systems that includemultiple processors.

Channel—a medium used to convey information from a sender (transmitter)to a receiver. It should be noted that since characteristics of the term“channel” may differ according to different wireless protocols, the term“channel” as used herein may be considered as being used in a mannerthat is consistent with the standard of the type of device withreference to which the term is used. In some standards, channel widthsmay be variable (e.g., depending on device capability, band conditions,etc.). For example, LTE may support scalable channel bandwidths from 1.4MHz to 20 MHz. In contrast, WLAN channels may be 20 MHz wide while asmaller bandwidth may be operated by populating a portion of thefrequency tones within a 20 MHz mask. Other protocols and standards mayinclude different definitions of channels. Furthermore, some standardsmay define and use multiple types of channels, e.g., different channelsfor uplink or downlink and/or different channels for different uses suchas data, control information, etc.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIG. 1—Communication System

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem. It is noted that the system of FIG. 1 is merely one example of apossible system, and embodiments of the disclosure may be implemented inany of various systems, as desired.

As shown, the example wireless communication system includes a cellularbase station 102 that may communicate over a transmission medium withone or more mobile devices 106A, 106N. Each of the mobile devices maybe, for example, a “user equipment” (UE) or other of various types ofdevices capable of wireless communication.

The base station 102 may be a base transceiver station (BTS) or cellsite, and may include hardware that enables wireless cellularcommunication with any or all of the UEs 106A through 106N. The basestation 102 may also be equipped to communicate with a network 100(e.g., a core network of a cellular service provider, atelecommunication network such as a public switched telephone network(PSTN), and/or the Internet, among various possibilities). Thus, thebase station 102 may facilitate communication between the mobile devicesand/or between the mobile devices and the network 100.

The communication area (or coverage area) of the base station may bereferred to as a “cell.” The base station 102 and the UEs 106 may beconfigured to communicate over the transmission medium using any ofvarious radio access technologies (RATs), also referred to as wirelesscommunication technologies, or telecommunication standards, such as GSM,UMTS (WCDMA, TD-SCDMA), LTE, LTE-Advanced (LTE-A), 3GPP2 CDMA2000 (e.g.,1×RTT, 1×EV-DO, HRPD, eHRPD), WLAN, WiMAX etc. A typical wirelesscellular communication system will include a plurality of cellular basestations which provide different coverage areas or cells, with handoffsbetween cells.

Additionally, the example wireless communication system may include oneor more wireless access points (such as access point 104) that may becommunicatively coupled to the network 100. Each wireless access point104 may provide a wireless local area network (WLAN) for communicationwith any or all of mobile devices 106 (e.g., UE 106B, as shown). Thesewireless access points may comprise WLAN access points. Wireless accesspoint 104 may be configured to support cellular network offloadingand/or otherwise provide wireless communication services as part of thewireless communication system illustrated in FIG. 1.

1) Cellular base station 102 and other similar base stations and 2)access points (such as access point 104) operating according to adifferent wireless communication standard may thus be provided as anetwork, which may provide continuous or nearly continuous overlappingservice any or all of the to mobile devices 106 and similar devices overa geographic area via one or more wireless communication standards.

Thus, while base station 102 may act as a “serving cell” for a UE 106 asillustrated in FIG. 1, any or all of the mobile devices 106 may also becapable of receiving signals from (and possibly within communicationrange of) one or more other cells (which might be provided by other basestations (not shown)) and/or wireless local area network (WLAN) accesspoints, which may be referred to as “neighboring cells” or “neighboringWLANs” (e.g., as appropriate), and/or more generally as “neighbors”.Further, two or more neighboring coverage areas may overlap to anydegree.

FIG. 2—Mobile Device Block Diagram

FIG. 2 illustrates an example simplified block diagram of a mobiledevice 106. As shown, the mobile device 106 may include a system on chip(SOC) 200, which may include portions for various purposes. The SOC 200may be coupled to various other circuits of the mobile device 106. Forexample, the mobile device 106 may include various types of memory(e.g., including NAND flash 210), a connector interface 220 (e.g., forcoupling to a computer system, dock, charging station, etc.), thedisplay 260, cellular communication circuitry 230 such as for LTE, GSM,etc., and short range wireless communication circuitry 229 (e.g.,Bluetooth™ and WLAN circuitry). The mobile device 106 may furtherinclude one or more smart cards 215 that provide SIM (SubscriberIdentity Module) functionality, such as one or more UICC(s) (UniversalIntegrated Circuit Card(s)) cards 215. The cellular communicationcircuitry 230 may couple to one or more antennas, for example to twoantennas 235 and 236 as shown. The short range wireless communicationcircuitry 229 may also couple to one or both of the antennas 235 and 236(this connectivity is not shown for ease of illustration).

As shown, the SOC 200 may include processor(s) 202, which may executeprogram instructions for the mobile device 106 and display circuitry204, which may perform graphics processing and provide display signalsto the display 260. The processor(s) 202 may also be coupled to memorymanagement unit (MMU) 240, which may be configured to receive addressesfrom the processor(s) 202 and translate those addresses to locations inmemory (e.g., memory 206, read only memory (ROM) 250, NAND flash memory210) and/or to other circuits or devices, such as the display circuitry204, cellular communication circuitry 230, short range wirelesscommunication circuitry 229, connector I/F 220, and/or display 260. TheMMU 240 may be configured to perform memory protection and page tabletranslation or set up. In some embodiments, the MMU 240 may be includedas a portion of the processor(s) 202.

In one embodiment, as noted above, the mobile device 106 includes atleast one smart card 215, such as a UICC 215, which executes one or moreSubscriber Identity Module (SIM) applications and/or otherwiseimplements SIM functionality. The smart card(s) 215 may be only a singlesmart card 215, or the mobile device 106 may include two or more smartcards 215. Each smart card 215 may be embedded, e.g., may be solderedonto a circuit board in the mobile device 106, or each smart card 215may be implemented as a removable smart card, an electronic SIM (eSIM),or any combination thereof. Any of various other SIM configurations arealso contemplated.

As noted above, the mobile device 106 may be configured to communicatewirelessly using multiple radio access technologies (RATs), e.g., usingone or more radios 229, 230. In general, a radio may include anycombination of a baseband processor, analog RF signal processingcircuitry (e.g., including filters, mixers, oscillators, amplifiers,etc.), or digital processing circuitry (e.g., for digital modulation aswell as other digital processing). Similarly, the radio may implementone or more receive and transmit chains using the aforementionedhardware. For example, the mobile device 106 may share one or more partsof a receive and/or transmit chain between multiple wirelesscommunication technologies, such as those discussed above.

The mobile device 106 may be configured to communicate according to aWLAN RAT and/or one or more cellular RATs, e.g., such as communicatingon both WLAN and cellular at the same time. For example, the mobiledevice 106 may be communicating on a primary communication channel (suchas WLAN), and in response to detected degradation of the primarycommunication channel may establish a secondary communication channel(such as on cellular). The mobile device 106 may operate to dynamicallyestablish and/or remove different primary and/or secondary communicationchannels as needed, e.g., to provide the best user experience whileattempting to minimize cost.

As described herein, the mobile device 106 may include hardware andsoftware components for implementing the features and methods describedherein. The processor 202 of the mobile device 106 may be configured toimplement part or all of the features described herein, e.g., byexecuting program instructions stored on a memory medium (e.g., anon-transitory computer-readable memory medium). Alternatively (or inaddition), processor 202 may be configured as a programmable hardwareelement, such as an FPGA (Field Programmable Gate Array), or as an ASIC(Application Specific Integrated Circuit). Alternatively (or inaddition) the processor 202 of the mobile device 106, in conjunctionwith one or more of the other components 200, 204, 206, 210, 215, 220,229, 230, 235, 236, 240, 250, 260 may be configured to implement part orall of the features described herein.

FIG. 3—Exemplary Block Diagram of an Access Point

FIG. 3 illustrates an example block diagram of an access point 104. Itis noted that the access point 104 of FIG. 3 is merely one example of apossible access point. As shown, the access point 104 may includeprocessor(s) 304 which may execute program instructions for the basestation 102. The processor(s) 304 may also be coupled to memorymanagement unit (MMU) 340, which may be configured to receive addressesfrom the processor(s) 304 and translate those addresses to locations inmemory (e.g., memory 360 and read only memory (ROM) 350) or to othercircuits or devices.

The access point 104 may include at least one network port 370. Thenetwork port 370 may be configured to couple to a network, such as theInternet, and provide a plurality of devices, such as mobile devices106, access to the network as described above in FIG. 1.

The network port 370 (or an additional network port) may also beconfigured to couple to a cellular network, e.g., a core network of acellular service provider. The core network may provide mobility relatedservices and/or other services to a plurality of devices, such as mobiledevices 106. In some cases, the network port 370 may couple to atelephone network via the core network, and/or the core network mayprovide a telephone network (e.g., among other mobile devices servicedby the cellular service provider).

The access point 104 may include at least one antenna 334, and possiblymultiple antennas. The antenna(s) 334 may be configured to operate as awireless transceiver and may be further configured to communicate withmobile devices 106 via radio 330. The antenna(s) 334 communicates withthe wireless communication circuitry 330 via communication chain 332.Communication chain 332 may be a receive chain, a transmit chain orboth. The radio 330 may be configured to communicate via variouswireless local area network standards, including, but not limited toWLAN.

The block diagram of FIG. 3 may also apply to cellular base station 102,except that communication may be performed using any of various cellularcommunication technologies instead of or in addition to WLAN.

FIG. 4—Flowchart

In order to support further deployment and usage as WLANs become morewidespread (e.g., both in cellular-WLAN interworking deployments andstandalone WLAN deployments, among various possible deploymentscenarios), increasing WLAN communication capacity (e.g., in terms ofincreasing throughput, user capacity, etc.) and flexibility is animportant consideration. One possible technique in support of thisconsideration may include introducing multi-user frame transmissions.Among the possible ways of providing such a multiple access feature, onepossible technique may include utilizing transmit beamforming togenerate orthogonal user signatures for the respective receivingdevices, such that a single physical protocol data unit (PPDU) frame canbe addressed to multiple users. However, this feature may requiremultiple antennas to provide beamforming capability.

As another possibility, orthogonal frequency division multiple access(OFDMA) may be used as a technique supporting simultaneous transmissionsto and/or from different devices, even for single antenna devices. FIG.4 is a flowchart diagram illustrating an example method for performingOFDMA communication in a WLAN, according to some embodiments. Aspects ofthe method of FIG. 4 may be implemented by a cellular base station,Wi-Fi access point, wireless user equipment device, or more generally inconjunction with any of the computer systems or devices shown in theabove Figures, among other devices, as desired.

In various embodiments, any of the elements of the method described maybe performed concurrently, in a different order than described, may besubstituted for by other method elements, or may be omitted. Additionalmethod elements may also be performed as desired. As shown, the methodmay operate as follows.

A first device may transmit a downlink OFDMA frame (402). The downlinkOFDMA frame may include one or more packets intended for each of(possibly) multiple receiving devices.

The downlink OFDMA frame may have a certain total bandwidth, in someembodiments. As one possibility, the bandwidth may be a multiple of 20MHz (e.g., 40 MHz, 60 MHz, 80 MHz, etc.), or subbands smaller than 20MHz. For example, the first frame may include a number of 20 MHzchannels or subbands (e.g., each having a 20 MHz transmit mask withguard bands between the channels) selected based on a number ofdestination stations for the first frame, an amount of data to betransmitted in the first frame, and/or any of various otherconsiderations. Other total bandwidths are also possible.

Additionally, the total bandwidth may be allocated to the variousreceiving devices, e.g., such that each packet is provided to itsdestination device on a particular channel or portion of the totalbandwidth. For example, following the above-described scenario in whichthe total bandwidth includes a number of fixed bandwidth (e.g., 20 MHz)channels, certain channel(s) may be intended for certain receivingdevice(s). The destination/intended recipient of the packet provided oneach channel/subband of the total bandwidth may be indicated inconjunction with the downlink OFDMA packet, for example by including adestination device identifier, such as a partial association ID (PAID),or any other format of STA ID, of the destination device, in the PHYpreamble of the downlink OFDMA frame on a per channel/subband basis, asone possibility. Note that in such a scenario, multiplechannels/subbands of the total bandwidth (which may not necessarily becontinuous in frequency) may be allocated to a single destinationdevice, if desired. Other frameworks for indicating which bandwidthportions (including frameworks in which dynamic/non-fixed bandwidthallocations are possible) are allocated to which receiving devices arealso possible.

At least in some embodiments, if the data/payload lengths are differentfor different bandwidth portions of the downlink OFDMA frame (e.g., fordifferent users/destination devices), padding (e.g., zeros appended tothe data) may be added to some or all of the data portions such thatsignals on all bandwidth portions of the total bandwidth are completedsimultaneously or substantially simultaneously. For example, a desiredpacket length (such as a packet length associated with the packet to betransmitted that has the longest payload portion) of each packetincluded in the downlink OFDMA frame may be determined, and the payloadof any packets less than that length may be padded to match the desiredpacket length.

In response to the downlink OFDMA frame, each respective recipient ofthe intended recipients of the downlink OFDMA frame may transmitacknowledgement information (e.g., indicating successful reception) ifthe data for the respective recipient is successfully received anddecoded. The first device may accordingly receive acknowledgementinformation from the recipient devices in response to the downlink OFDMAframe (404).

The acknowledgement information may be received concurrently by thefirst device as an uplink OFDMA frame. For example, as noted above, bymatching the length of the packets transmitted as part of the downlinkOFDMA frame, the signals transmitted on the various portions (e.g.,channels) of the downlink OFDMA frame may terminate in a timesynchronized manner, and this time synchronization may in turnfacilitate/coordinate potential time synchronous reception ofacknowledgement information from the various devices receiving thedownlink OFDMA frame, such that the acknowledgement information mayeffectively be received as an uplink OFDMA frame.

The first device may process the acknowledgement information (e.g., inparallel, or serially if desired) received to determine which of thereceiving devices transmitted acknowledgements (406). At least in someinstances, each receiving device may provide an acknowledgement (ifsuccessful at decoding its packet(s)) using the same bandwidth portionon which the packet(s) being acknowledged was/were received. It is alsopossible that a receiving device that was allocated multiple channels orbandwidth portions may choose to provide an acknowledgement on a subsetof the bandwidth allocated to it for the first frame; for example, adevice allocated multiple 20 MHz channels might provide anacknowledgement for all of its allocated channels using just one ofthose channels or fewer than all allocated channels.

Timing alignment for the uplink OFDMA frame may be sufficiently providedfor by the packet length matching of the downlink OFDMA frame and byreceiving devices using a consistent and predictable time interval(e.g., a short interframe space (SIFS)) between packet reception andacknowledgement transmission, at least in some embodiments. Accordingly,the first device may be able to perform carrier sensing to detect theuplink OFDMA frame using autocorrelation over the total bandwidth of theuplink OFDMA frame (which may be the same as the total bandwidth of thedownlink OFDMA frame, e.g., if acknowledgements are transmitted usingthe same bandwidth portions as are used in the downlink OFDMA frame).Automatic gain control (AGC) may also be set based on suchautocorrerlation over the total bandwidth, in some embodiments.

Techniques may also be implemented to estimate and correct thepotentially different frequency offsets of different receiving devicesas part of processing the acknowledgement information. For example, asone possibility, coarse carrier frequency offset (CFO) estimation andcorrection may be performed over the total bandwidth of the uplink OFDMAframe, e.g., using the legacy short training field (L-STF) of the uplinkOFDMA frame. Subsequently, the various portions (e.g.,channels/subbands) of the total bandwidth may be separated out, forexample, using Fourier transform techniques. Fine CFO estimation andcorrection may then be performed separately for each of multipleportions (e.g., for each portion associated with a different receivingdevice) of the total bandwidth of the uplink OFDMA frame, e.g., usingthe legacy long training field (L-LTF) of the uplink OFDMA frame. Basedon such channel and CFO estimation and correction, the first device maythen perform tone mapping, deinterleaving, and decoding of any remainingPHY preamble fields (e.g., L-SIG) and the payload (e.g., acknowledgementinformation) for each of the multiple portions of the total bandwidth ofthe uplink OFDMA frame.

FIGS. 5-13

FIGS. 5-13 and the information provided herein below in conjunctiontherewith are provided by way of example of various considerations anddetails relating to possible systems in which the method of FIG. 4and/or other aspects of this disclosure may be implemented, and are notintended to be limiting to the disclosure as a whole. Numerousvariations and alternatives to the details provided herein below arepossible and should be considered within the scope of the disclosure.

IEEE 802.11 is a set of media access control (MAC) and physical layer(PHY) specifications for implementing WLAN communication. 802.11acintroduced a new feature for downlink multi-user frame transmissions(downlink MU-MIMO) where frames addressed to several users (up to amaximum of 4) may be transmitted simultaneously in a single PPDU frame.Based on transmit beam forming, orthogonal user signatures are generatedby the transmitting device using multiple antennas. However, thisfeature cannot be enabled if the transmitter has a single antenna.

Orthogonal Frequency Division Multiple Access (OFDMA) may be useful inoptimizing bandwidth use for WLAN communication. OFDMA may be useful fortransmitters having a single antenna, e.g., allowing simultaneoustransmissions to/from different users even if the transmitting device isa single antenna device.

In some embodiments, downlink OFDMA may be implemented and may beindicated by using one or more bits in a PHY signal field and/or using atrigger frame, among other possibilities. For example, a new bit in thePHY signal field may indicate that the current frame is beingtransmitted in OFDMA mode. Additionally, an OFDMA PHY structure may beimplemented for handling communications to and/or from multiplerecipients.

In some embodiments, as shown in FIG. 5, the OFDMA mode may operate inunits of 20 MHz (e.g., resource block size=20 MHz) with 20 MHz spectraltransmit mask. However, it should be noted that the 20 MHz size isexemplary only, and others are envisioned, such as 2.5, 5, 10, 15, 30,40, 60, 80, 100, or other values. The total bandwidth in this example isshown as 80 MHz (e.g., including four 20 MHz channels 502, 504, 506,508), although other values of the total bandwidth are also envisioned.

OFDMA may also be implemented in the uplink in WLANs. For example, eachreceiving device (e.g., mobile devices) may provide acknowledgementsback to the transmitting device (e.g., the AP) as a response to downlinkpackets. Note that while various embodiments may be particularly usefulwhere an AP transmits to a plurality of mobile devices, situations wherea mobile device transmits to multiple mobile devices and/or the AP arealso envisioned.

In some embodiments, in order to ensure that acknowledgements from thereceiving devices are transmitted at the same time, the OFDMA packetsoriginally sent to the receiving devices may be the same size. Forexample, the transmitting device may “pad” the transmitted packets(e.g., with “0” s or some other sequence of bits) in order to ensurethat all the packets are the same size (e.g., padding each payload tothe size of the largest payload in the group). By ensuring the samesize, time synchronization of the acknowledgements may be achieved.

In addition to addressing the time synchronization, a frequency offsetestimation and correction algorithm for uplink OFDMA may be implementedby the device which is receiving the acknowledgements from the multipledevices simultaneously.

FIG. 6 illustrates a frequency/time diagram of an example transmissionin the downlink 602 and acknowledgement in the uplink 604. In thisinstance, the device assigned to the second band 608 has the longestpayload, and has no additional padding. The payloads of the first band606, third band 610, and fourth band 612 are padded to match the size ofthe second band's payload. The transmitted packets may include legacy,HEW-SIG, and HEW preamble fields, according to some embodiments. After aSIFS 614, the receiving devices that successfully decoded thetransmitted packets (in this instance, the first, second, and fourthreceiving devices) transmit acknowledgements to the transmitting device.

In this example, the downlink OFDMA transmission 602 is performed as aunit of 20 MHz bands per user. However, as noted above, this band sizecould be smaller or larger than 20 MHz (scalable), as desired. Theuplink OFDMA packets (ACKs) 604 may keep the same bandwidth asresponses, or operate in different size of bandwidth, e.g., that may bedynamically assigned by the transmitting device. As noted above, if thepacket length is different per user, some or all of the packets may bepadded (e.g., with zeros) such that the transmissions have the samelength. Upon reception of a downlink OFDMA packet, each recipient maysend back an ACK after the SIFS 614, e.g., using the same band ofoperation. If the packet reception fails, the recipient may not send anACK. In general, the ACKs may be sent at the same time, e.g., uponexpiration of the SIFS 614 after the end of the received OFDMA packet602. Note that if signals are sent simultaneously or nearlysimultaneously to a STA on more than one 20 MHz band, the STA may sendan ACK on any or all of the separate 20 MHz bands used.

FIG. 7 illustrates an exemplary time/frequency diagram of theacknowledgements. In this example, the transmitter (e.g., the AP) mayexpect to receive ACKs for each of the 20 MHz bands 702, 704, 706, 708after a SIFS interval following the end of a downlink OFDMA packet. Thelegacy portions of preamble may be identical and arrive simultaneouslywithin the cyclic prefix (CP) period. The total BW of ACKs may be thesame as with the BW of the downlink OFDMA packet, therefore thetransmitter may know which BW filter to use (e.g., in this example, 80MHz). The packet detection and processing of the preamble is discussedin more detail below.

Processing the L-STF may involve single processing over the total BW.Using auto-correlation over the total BW, the transmitting devicereceiving the acknowledgements may perform CS (carrier sense) for packetdetection 710 and set AGC (automatic gain control). In one embodiment,within 8 usec (e.g., the length of two OFDM symbols), the transmittingdevice receiving the acknowledgements may turn on Fast Fourier Transform(FFT) and Carrier Frequency Offset (CFO) modules.

Processing the L-LTF may involve single processing for channelestimation and parallel processing for CFO estimation and correction. Inone embodiment, 256 FFT (64×4 for 80 MHz) may be performed to separateout each 20 MHz band. CFO estimation and correction 712 may be processedfor each 20 MHz band. Additionally, channel estimation 714 may beperformed for each 20 MHz band. The transmitting device receiving theacknowledgements may identify which 20 MHz band is empty (i.e., where noACKs were received).

Processing the L-SIG and payload may involve parallel processing of thedata, e.g., per 20 MHz band. In some embodiments, any or all of tonemapping, deinterleaving, and decoding can be performed, e.g., per 20 MHzband.

FIG. 8 illustrates a waveform diagram related to preamble processing ofan UL-OFDMA packet. The packet arrival time is well synchronized withthe SIFS time interval (e.g., due to padding discussed above).Accordingly, it is possible to detect the packet using autocorrelation802. Estimating and/or correcting the frequency offset (including coarsefrequency offset estimation 804 and fine frequency offset estimation806) may also be performed, as the frequency offset can differ per user.

FIGS. 9A-B illustrate autocorrelation performed at the L-STF portion. Inparticular, FIG. 9A illustrates an example of possible L-STF signals ofan acknowledgement UL-OFDMA frame, while FIG. 9B illustratesautocorrelation results for the L-STF signals of FIG. 9A. Within theSIFS period following a downlink OFDMA packet, the transmitting devicemay expect to receive multiple ACKs at different frequency bands;however, it may not know which STAs will send an ACK (e.g., which mobiledevices successfully decoded the transmission and transmittedacknowledgements). The transmitting device may collect the first 0.8usec of samples and perform auto-correlation. If it shows repeatedpattern (such as illustrated in FIG. 9A, e.g., 902, 904, 906, etc.), thetransmitting device (e.g., the AP) is receiving ACKs. Although some ACKsmay be missing at some frequency bands (e.g., an ACK is missing at thethird frequency band in the example of FIGS. 9A-B), L-STFs will stillshow a repeated autocorrelation pattern (such as illustrated in FIG. 9B,e.g., including peaks 908, 910, etc.) if other ACKs are present. Notethat if extra memory is available at the transmitting device, it may beconfigured to recognize in which frequency bands an ACK is missing byperforming cross-checks of the L-STF pattern(s), e.g., against allpossible L-STF patterns.

After a packet is detected, a frequency offset may be estimated andcorrected. The CFO estimation range may be limited by the length of therepeated sequence. More specifically, the estimation range may beinversely proportional to the sequence length. The L-STF sequence mayhave a length of 0.8 us and the L-LTF sequence may have a length of 3.2us, according to some embodiments. Thus, estimation using the L-STFsequence may have a larger range (625 kHz) but a shorter period (Ns).Accordingly, the L-STF estimation can provide lower accuracy (e.g., acoarse estimate). Estimation using the L-LTF sequence has a shorterrange (156.2 kHz) but a longer period (Ns). Thus, the L-LTF estimationcan provide higher accuracy (e.g., a fine estimate).

Coarse CFO estimation/correction may be performed over the last twoL-STF sequences of the 80 MHz time domain signal. The correction may beperformed over the full 80 MHz time domain signal.

Fine CFO estimation/correction may be performed in the frequency domainover the L-LTF. Correction may be performed in the time domainseparately for each 20 MHz band. Fine CFO estimation/correction may beused in addition to coarse CFO estimation/correction to estimate/correctresidual CFO estimation error for each 20 MHz signal, e.g., due to thediffering CFOs of different STAs.

FIG. 10 illustrates frequency offset estimation and correction per user.Down conversion 1002 may be performed to remove the carrier frequency(2.4 GHz or 5 GHz). Coarse Frequency Correction 1004 may apply thevalues estimated using the last two L-STF fields, e.g., using thefollowing equation:e ^(−j2πεn/N)where:

M: The number of users (4 in this example)

N: The total number of FFT size (256 in this example)

Y_(j,k): received samples at jth OFDM symbol at kth tone

ε_(i): estimated frequency offset for ith user:

${\hat{ɛ}}_{i} = {{\frac{1}{2\pi}{\tan^{- 1}\left\lbrack \frac{\sum\limits_{k = {{({i - 1})}{N/M}}}^{{iN}/M}\;{{Im}\left( {Y_{2,k}Y_{1,k}^{*}} \right)}}{\sum\limits_{k = {{({i - 1})}{N/M}}}^{\frac{iN}{M} - 1}\;{{Re}\left( {Y_{2,k}Y_{1,k}^{*}} \right)}} \right\rbrack}} = {\frac{1}{2\pi}\arg\;\left( {\sum\limits_{k = {{({i - 1})}{N/M}}}^{\frac{iN}{M} - 1}\;\left( {Y_{2,k}Y_{1,k}^{*}} \right)} \right)}}$

Fine Frequency Correction 1006 may apply residual offset values, whichcan be estimated per band, using two L-LTF fields, e.g., using thefollowing equation:e ^(−j2πε) ^(i) ^(n/N)

FIG. 11 illustrates a logical block diagram for CFO estimation in anexample scenario with an 80 MHz signal bandwidth including four 20 MHzchannels, each allocated to a different user. As shown, coarse CFOestimation and correction (1102) may be applied over the totalbandwidth. 256 FFT (1104) and fine CFO estimation (1106) may then befollowed by fine CFO correction (1108, 1110, 1112, 1114) on a per-userbasis. Per-user 256 FFT (1116, 1118, 1120, 1122) may then be applied andthe subcarriers for each user may be processed. It is noted thatprocessing can be modified in some implementations, e.g., by using adifferent FFT size or by performing additional/different operations.

FIG. 12 illustrates an example of frequency offset correction for binaryphase shift keying (BPSK) modulation in which H=1. In this example,samples having randomized phase due to frequency offset per user 1202are corrected using L-STF (coarse offset corrected 1204) then L-LTF(offset corrected 1206) in a manner similar to that discussed hereinabove. The plot of FIG. 12 illustrates results.

FIG. 13 illustrates example cumulative distribution function (CDF) plotsof channel estimation with frequency offset correction. In theseexamples, frequency offsets from four users are randomized uniformly in[−20, 20] ppm. Frequency offsets may be estimated and the correction isapplied differently in each band per user. The graphs of FIG. 13illustrate operating results. As shown, there are CDF plots at each ofvarious signal to noise ratios (SNRs), including 10 dB 1302, 20 dB 1304,30 dB 1306, and 40 dB 1308.

In the following further exemplary embodiments are provided.

One set of embodiments may include a method for performing OFDMAcommunication in a WLAN, including: at a transmitting device:transmitting first information to multiple receiving devices over theWLAN indicating that a current frame is an OFDMA frame; transmittingsecond information to each of the multiple receiving devices indicatingrespective channel information regarding one or more channels of theWLAN bandwidth associated with the respective receiving device;transmitting data to each of the multiple receiving devices according tothe channel information comprised in the second information.

According to some embodiments, the transmitting device includes anaccess point.

According to some embodiments, the first information is included in thecurrent frame in the signal field.

According to some embodiments, the first information is included in aseparate frame that is sent in advance.

According to some embodiments, the signal field indicates modulation andcoding information.

According to some embodiments, the signal field indicates allocatedbandwidth information.

According to some embodiments, the signal field includes informationidentifying the respective device.

According to some embodiments, the information identifying therespective device includes a partial association ID (PAID) or otherformat of STA ID.

A further set of embodiments may include a transmitting device,configured to perform the method of any of the preceding examples,including: at least one antenna; a first radio, wherein the first radiois configured to perform WLAN communication with the plurality ofreceiving devices; and at least one processor coupled to the firstradios.

A still further set of embodiments may include a non-transitory,computer accessible memory medium storing program instructionsexecutable to perform a method according to any of the precedingexamples.

Yet another set of embodiments may include a method for performing OFDMAcommunication in a WLAN, including: at a transmitting device:determining a desired packet length for a transmission to multiplereceiving devices; generating a packet for each of the multiplereceiving devices having the desired packet length; concurrentlytransmitting the plurality of packets to the receiving devices usingOFDMA; and receiving information including a plurality ofacknowledgements from the receiving devices corresponding to theplurality of packets transmitted to the receiving devices, wherein theplurality of acknowledgements were transmitted concurrently; andprocessing the information to determine which of the receiving devicestransmitted acknowledgements.

According to some embodiments, generating the packet includes padding aplurality of packets to match the desired packet length.

According to some embodiments, padding the plurality of packetscomprises adding 0s to the data to match the desired packet length.

Embodiments of the present application may be realized in any of variousforms. For example, various described embodiments may be realized as acomputer-implemented method, a computer-readable memory medium, or acomputer system. In other embodiments, the present invention may berealized using one or more custom-designed hardware devices such asASICs. In other embodiments, the present invention may be realized usingone or more programmable hardware elements such as FPGAs. For example,some or all of the units included in the UE may be implemented as ASICs,FPGAs, or any other suitable hardware components or modules.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE 106) may be configured toinclude a processor (or a set of processors) and a memory medium, wherethe memory medium stores program instructions, where the processor isconfigured to read and execute the program instructions from the memorymedium, where the program instructions are executable to implement anyof the various method embodiments described herein (or, any combinationof the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of suchsubsets). The device may be realized in any of various forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A wireless device, comprising: an antenna; aradio operably coupled to the antenna; and a processing element operablycoupled to the radio; wherein the wireless device is configured to:transmit a downlink orthogonal frequency division multiple access(OFDMA) frame to a plurality of receiving devices, wherein the downlinkOFDMA frame comprises one or more packets intended for each respectivereceiving device of the plurality of receiving devices; receive anuplink OFDMA frame, wherein the uplink OFDMA frame comprises a pluralityof acknowledgements associated with the downlink OFDMA frame, whereinthe plurality of acknowledgements comprise an acknowledgement from atleast a subset of the plurality of receiving devices; and process theuplink OFDMA frame, comprising determining which of the plurality ofreceiving devices transmitted, in the uplink OFDMA frame, anacknowledgement associated with the downlink OFDMA frame, wherein packetlengths of the packets included in the downlink OFDMA frame areconfigured to have equal length across a total bandwidth of the downlinkOFDMA frame to coordinate timing synchronization of the acknowledgementsincluded in the uplink OFDMA frame.
 2. The wireless device of claim 1,wherein the wireless device is further configured to: determine a totalbandwidth of the uplink OFDMA frame based on a total bandwidth of thedownlink OFDMA frame; and configure a bandwidth filter for performingcarrier sensing for the uplink OFDMA frame to correspond with thedetermined total bandwidth of the uplink OFDMA frame.
 3. The wirelessdevice of claim 1, wherein to process the uplink OFDMA frame, thewireless device is further configured to: perform carrier sensing todetect the uplink OFDMA frame using autocorrelation over a totalbandwidth of the uplink OFDMA frame; and configure automatic gaincontrol for the uplink OFDMA frame using autocorrelation over the totalbandwidth of the uplink OFDMA frame.
 4. The wireless device of claim 1,wherein to process the uplink OFDMA frame, the wireless device isfurther configured to: perform a first frequency offset estimation andcorrection operation for the uplink OFDMA frame, wherein the firstfrequency offset estimation and correction operation is performed on atime domain signal received over a total bandwidth of the uplink OFDMAframe; and perform second frequency offset estimation and correctionoperations for the uplink OFDMA frame, wherein a second frequency offsetestimation and correction operation is performed on each of a pluralityof portions of the time domain signal received over the total bandwidthof the uplink OFDMA frame.
 5. The wireless device of claim 4, whereinthe first frequency offset estimation and correction operation uses alegacy short training field (L-STF) of the uplink OFDMA frame, whereinthe second frequency offset estimation and correction operations use alegacy long training field (L-LTF) of the uplink OFDMA frame.
 6. Thewireless device of claim 4, wherein the wireless device is furtherconfigured to: separate the time domain signal received over the totalbandwidth of the uplink OFDMA frame into the plurality of portions usinga Fourier transform operation.
 7. The wireless device of claim 1,wherein the downlink OFDMA frame comprises a total bandwidth, wherein arespective portion of the total bandwidth is allocated to eachrespective receiving device of the plurality of receiving devices forthe downlink OFDMA frame, wherein the uplink OFDMA frame also comprisesthe total bandwidth, wherein each respective acknowledgment of theplurality of acknowledgements is received on the respective portion ofthe total bandwidth allocated to the receiving device associated withthe respective acknowledgement.
 8. A method for performing orthogonalfrequency division multiple access (OFDMA) communication in a wirelesslocal area network (WLAN), comprising: at a first device: transmitting adownlink orthogonal frequency division multiple access (OFDMA) frameover the WLAN, wherein the downlink OFDMA frame comprises packetstransmitted to a plurality of second devices; receiving an uplink OFDMAframe over the WLAN in response to the downlink OFDMA frame, wherein theuplink OFDMA frame comprises packets received from the plurality ofsecond devices; and processing the uplink OFDMA frame, comprisingdecoding the packets received from the plurality of second devices,wherein packet lengths of the packets included in the downlink OFDMAframe are configured to have equal length across a total bandwidth ofthe downlink OFDMA frame to coordinate timing synchronization of thepackets included in the uplink OFDMA frame.
 9. The method of claim 8,wherein the packets received from the plurality of second devicescomprise acknowledgements associated with the packets transmitted to theplurality of second devices in the downlink OFDMA frame, whereinprocessing the uplink OFDMA frame further comprises determining which ofthe plurality of second devices transmitted an acknowledgement in theuplink OFDMA frame.
 10. The method of claim 8, wherein configuringpacket lengths of the packets included in the downlink OFDMA frame tohave equal length across the total bandwidth of the downlink OFDMA framecomprises padding at least one packet included in the downlink OFDMAframe.
 11. The method of claim 8, wherein the downlink OFDMA frame andthe uplink OFDMA frame have equal total bandwidth, wherein each packetincluded in the downlink OFDMA frame is transmitted on a band associatedwith the total bandwidth, wherein each packet included in the uplinkOFDMA frame is received on a same band as that on which an associatedpacket included in the downlink OFDMA frame is transmitted.
 12. Themethod of claim 8, wherein processing the uplink OFDMA frame furthercomprises: performing carrier sensing and setting automatic gain controlfor the uplink OFDMA frame based on autocorrelation over a totalbandwidth of the uplink OFDMA frame; performing channel estimation andcarrier frequency offset estimation and correction for each of aplurality of subbands of the total bandwidth of the uplink OFDMA frame,wherein each of the plurality of subbands is associated with arespective second device of the plurality of second devices; andperforming tone mapping, deinterleaving, and decoding for each of theplurality of subbands using the channel estimation and carrier frequencyoffset estimation and correction for each of the plurality of subbands.13. An apparatus, comprising a processing element configured to cause awireless device to: determine a target packet length for a transmissionto a plurality of receiving devices; generate a plurality of packets,wherein the plurality of packets comprise a packet for each of theplurality of receiving devices, wherein each packet has the targetpacket length; concurrently transmit the plurality of packets to theplurality of receiving devices as a downlink orthogonal frequencydivision multiple access (OFDMA) frame; receive information comprising aplurality of acknowledgements from the plurality of receiving devicescorresponding to the plurality of packets transmitted to the pluralityof receiving devices, wherein the plurality of acknowledgements weretransmitted concurrently; and process the information to determine whichof the plurality of receiving devices transmitted acknowledgements,wherein generating the plurality of packets such that each packet hasthe target packet length and concurrently transmitting the plurality ofpackets to the plurality of receiving devices as a downlink OFDMA frameprovides timing synchronization for the plurality of acknowledgements tobe received as an uplink OFDMA frame.
 14. The apparatus of claim 13,wherein at least one of the plurality of packets is padded to match thetarget packet length.
 15. The apparatus of claim 13, wherein each packetof the plurality of packets is transmitted on a different portion of atotal bandwidth associated with the downlink OFDMA frame, and whereineach respective acknowledgement of the plurality of acknowledgements isreceived on a same band of the total bandwidth of the downlink OFDMAframe as a packet to which the respective acknowledgement corresponds istransmitted.
 16. The apparatus of claim 13, wherein the processingelement is further configured to cause the wireless device to: detectthe information comprising a plurality of acknowledgements as an uplinkOFDMA frame using autocorrelation over a total bandwidth of the uplinkOFDMA frame.
 17. The apparatus of claim 16, wherein the processingelement is further configured to cause the wireless device to: performcoarse frequency offset estimation and correction for the uplink OFDMAframe over the total bandwidth of the uplink OFDMA frame; and performfine frequency offset estimation and correction for the uplink OFDMAframe separately for each of a plurality of portions of the totalbandwidth of the uplink OFDMA frame.
 18. The wireless device of claim 1,wherein configuring the packet lengths comprises padding at least onepacket.
 19. The wireless device of claim 1, further configured toperform carrier sensing and set automatic gain control for the uplinkOFDMA frame based on autocorrelation over a total bandwidth of theuplink OFDMA frame.
 20. The apparatus of claim 13, wherein theprocessing element is further configured to cause the wireless device toperform carrier sensing and set automatic gain control for the uplinkOFDMA frame based on autocorrelation over a total bandwidth of theuplink OFDMA frame.